Eastern Australia DH8C at Mildura on Jun 6th 2023, near collision on runway with private aircraft

Last Update: May 14, 2024 / 13:13:33 GMT/Zulu time

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Incident Facts

Date of incident
Jun 6, 2023

Classification
Report

Flight number
QF-1402

Aircraft Registration
VH-TQH

ICAO Type Designator
DH8C

An Eastern Australia de Havilland Dash 8-300 on behalf of Qantas, registration VH-TQH performing flight QF-1402 from Mildura,VI to Sydney,NS (Australia) with 33 passengers and 3 crew, was taxiing for departure from runway 09 backtracking the runway, turning around and commencing takeoff from runway 09.

A private Piper PA-28 had also been taxiing for departure from runway 36, lined up and shortly after QF-1402 commenced their takeoff began their takeoff run from runway 36.

When the Dash 8 crossed the intersection of the two runways at 200 feet AGL, the PA-26 was about 600 meters/2000 feet ahead of the runway intersection.

Australia's TSB released their final report into the serious incident labelled "near collision" concluding the probable causes were:

Contributing factors

- Both aircraft crews had incorrect mental models of local traffic at Mildura and neither crew spoke directly to the other to ascertain position and intentions before take-off.

- Both Dash 8 crew were focussed on receiving the final information from air traffic control when the CTAF broadcast from the other aircraft occurred, and the volume for the radio tuned to the CTAF frequency had been turned down. Their focus and reduced radio volume, and an over transmission, likely led to an incomplete comprehension of traffic at Mildura during the time compressed phase of pre-departure.

- Due to topography and buildings at Mildura Airport, aircraft are not directly visible to each other on the threshold of runway 09, 27 and 36. The lack of a requirement for mandatory rolling calls increased the risk of aircraft not being aware of each other immediately prior to take-off.

- The Dash 8 crew assumed there was no traffic at Mildura and elected to not make a rolling call on runway 09 before take-off. The PA 28 pilot was aware that the Dash 8 was backtracking, but was not aware it had begun its take-off roll.

- The PA-28 pilot broadcasted an incorrect runway direction for Mildura Airport in both the 'taxiing' and 'entering and backtracking' radio calls.

Other findings

- The crew of the Dash 8 monitored the other aircraft after the occurrence to ensure their safety and render assistance if required.

The ATSB summarized the sequence of events:

In the early afternoon of 6 June 2023, a Piper PA-28-161 (PA-28), registered VH-ENL taxied for runway 361 at Mildura, New South Wales, for a private flight to Broken Hill (Figure 1 orange line).

The pilot was the sole occupant. At about the same time, a QantasLink Bombardier DHC-8-315 (Dash 8), registered VH-TQH, with 3 crew and 33 passengers on board, being operated on a scheduled passenger transport flight to Sydney, began to taxi at Mildura for runway 09 (Figure 1 blue line).

Both aircraft gave taxi, runway entering and runway backtracking calls on the local common traffic advisory frequency (CTAF) (see Radio calls). The pilot of the PA-28 was aware of the Dash 8 backtracking on runway 09, however the crew of the Dash 8 were not aware of the PA-28 preparing for take-off on the cross runway.

The Dash 8 had started its take off roll on runway 09 as the PA-28 gave a rolling call on runway 36 and commenced take-off. As the Dash 8 crossed the runway intersection of 09/36 at about 200 ft vertically, the PA-28 was rolling towards the intersection and about 600 m from the Dash 8 (Figure 1 aircraft positions).


The ATSB analysed:

Succinct and timely radio communication is important to ensuring high levels of situational awareness and aids in providing alerted see-and-avoid safety outcomes. As such, the accuracy of the information broadcast by pilots is also critical in ensuring minimum misunderstanding.

The use of a standard phraseology format is an important factor to increase the effectiveness of radio communication and to prevent misunderstanding. It also increases the attentional expectation of pilots to recognise key phraseology in the cockpit to determine the significance of the information to their operations.

However, these communications can be subject to human error, even when it involves experienced pilots. In this instance, the pilot of the PA-28 unknowingly announced an incorrect runway direction designator (runway 35 instead of runway 36) on 2 separate occasions which introduced confusion and led the Dash 8 crew to incorrectly deduce that the transmission did not originate from Mildura.

During one of the busiest parts of passenger transport operations from a non-controlled aerodrome, the crew of the Dash 8 had difficulty in receiving a transponder code for their departure from Mildura. Controllers had difficulty finding the code due to the 6-hour mechanical delay from the original flight plan and their response also coincided with the taxi call from the PA-28 pilot.

This added complexity within a busy phase of pre-departure, and likely led to additional attentional focus on obtaining the departure code to the exclusion of effective situational awareness and the monitoring of other traffic on the CTAF. Such focus can reduce the chance of hearing and appreciating the relevance of other radio broadcasts.

In addition, the volume on the aircraft radio that was tuned to the Mildura CTAF was turned down (likely to facilitate the crew’s focus on receiving the pre-departure transponder code). This would have further reduced the likelihood of the crew noticing the PA-28 broadcasts.

Although the operator suggested VHF radio shielding may have affected the receipt of the PA-28 radio call by the Dash 8 crew, the ATSB had no direct evidence of such radio shielding. However, even if radio shielding was possible at Mildura Airport, the above explained over transmission, focus of attention and radio volume in this occurrence likely contributed to the Dash 8 crew not fully comprehending the PA-28 broadcasts.

Local traffic mental model and runway threshold visibility

The circumstances and the restrictions imposed on the available electronic aids, particularly TCAS functionality, were impediments to effectively applying alerted see-and-avoid practices.

The crew of the Dash 8 were not aware of the presence of the PA-28 as a threat to their operation. Although visibility was greater than 10 km with no cloud in the area, visual searches prior to take-off on runway 09 for other conflicting traffic were likely obscured by obstacles such as trees, hangars and buildings between the threshold of runway 09 and runway 36.

In many instances the conduct of a rolling call on the runway is given by pilots to increase the situational awareness of other traffic, however if there is no identified traffic that may cause a hazard at the airport, a pilot is not required to make a rolling call.

However, other traffic may be expecting such a call, in order to update their mental model of traffic in the vicinity of the aerodrome, especially where visual identification of traffic is limited.

The pilot of the PA-28 received and understood the calls from the Dash 8, however believed that the aircraft was still backtracking on runway 09 as they had not heard, but were expecting, the Dash 8 to give a rolling call. Visual identification of the location of the Dash 8 backtracking on runway 09 was not possible from the threshold of runway 36 and therefore reduced the effectiveness of the alerted see-and-avoid principle.

This resulted in both crew of the Dash 8 and the pilot of the PA-28 having incorrect mental models of the local traffic at Mildura during their take-off. While each of the pilots made assumptions as to local traffic location and intentions, neither tried to contact the other directly to positively ascertain traffic separation, resulting in a missed opportunity to utilise the mitigation of alerted see-and-avoid effectively.

Rolling calls at Mildura Airport

While take-off rolling calls are not required when there is no identified traffic, this is based on the situational awareness of flight crew and may not always be correct at airports where visual identification of other traffic is limited by buildings, terrain or vegetation. At Mildura Airport, it has been established that when two aircraft are at the thresholds of runway 09 and 36, they are not visible to each other due to buildings and trees. Similarly, two aircraft at either end of runway 09/27 intending to take-off will not be visible to each other due to central runway elevation.

While the lack of visibility may be recognised by some pilots and prompt them to make a take-off rolling call, a lack of awareness of another aircraft will not prompt the pilot to think about the possibility of another aircraft. As such, a reliance on an extra broadcast through recognition of the lack of visibility will often be ineffective, especially when there is no expectation of another aircraft.

Airports can mandate additional broadcasts where there is a need, such as a rolling call to improve flight crew situational awareness of conflicting traffic when there are visibility limitations.

However, although Mildura Airport had recognised that aircraft may not be visible to each other on the runway and had this noted in the Enroute Supplement Australia (ERSA), they had not mandated additional radio calls.

Airmanship

After take-off the crew of VH-TQH made contact with the pilot of VH-ENL, partly to establish the communication breakdown, but also to check on the welfare of the other pilot after the incident and if required render any additional airborne support to the pilot after the occurrence.
Incident Facts

Date of incident
Jun 6, 2023

Classification
Report

Flight number
QF-1402

Aircraft Registration
VH-TQH

ICAO Type Designator
DH8C

This article is published under license from Avherald.com. © of text by Avherald.com.
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